Hello, first of all thank you for your help and ideas.

I have to measure water and gas consumption using some of the several flow sensors available in the market.

The question that appear when I have to choose one technology among all others is communications protocol (4-20mA flow measurements proportional to current in the loop, or a pulse pattern).

The main requirement is to make this measurement available in a modbus network (1 register for total consumption and other register for the rate of flow change)

4-20mA; it will require a proper calibration and a controller to estimate the cumulative water/gas used so far.

Pulse pattern: it will require a pulse counter and a frequency pulse meter, both variable will have to be available as a typical modbus slave device

from your experience: which is the best solution considering low cost implementation, cabling, and reliability

Thank you

 

> I have to measure water and gas consumption using some of the several
> flow sensors available in the market.

The pulse meter will give you the amount of material pass through over time and compute back the average rate of flow.

The 4-20mA give you the real-time rate of flow and compute back the amount of material used.

There are low-cost Modbus TCP devices for both pulse and 4-20mA from lowcostio.com to try out.

The Free50 License SCADA software to do data logging, then, compute back both rate of flow or amount of material used can be see the example from http://www.lowcostsystem.blogspot.com/2012/02/how-to-develop-low-cost-online.html

 

For someone just starting out with Modbus, I'd suggest the pulse counter. Current loop is loads of fun, but pulses are more fool-proof. And, as you pointed out, you have to derive the other piece of information -- either current flow (from pulse devices) or cumulative flow (from current loop devices).

The other useful consideration is that pulse counting is less prone to problems with creep -- unless the current is 4.000ma, and the recording device measures it as 4.000ma, there may be creep in the indicated value. With pulse counters, no pulse, no flow. You must may have to wait a while for a pulse to tell you the flow rate is REALLY REALLY SLOW